Method of making plastic springs



May 8, 1945. v Q 1 T. FR|EDMA N 4 2,375,357

METHOD OF MAKING A PLASTIC SPRING Filed March 51, 194:5

' I IN VEN TOR. "7/15 000/? f FR/fD/Vfl ATTORNEY Patented May 8', 1945 UNITED fiTATES PATENT OFFICE -METHOD OF MAKING PLASTIC SPRINGS Theodore Friedman, New York, N. Y. Application March 31, 1943, Serial No. 481,349

4 Claims.

This invention relates to amethod of making plastic springs'and has as its main object the provision of an economical, efllcient and practical helical or spiral spring made of plasticmaterial and offering a good substitute for they conventional metal spring.

Heretofore, it has been customary to construct spiral springs out of metal. However, such material is costly and particularly at the present time there is a great scarcity of metal due-to the restrictions placed on the use thereof by the- United States Government, because of the present demand for metal needed for the War effort. It has been found that by making a spiral spring out of either thermoplastic or thermcset ting material an instrumentality is provided which has sufllcient resiliency such that when stretched, it will return to its original spiral form.

tubular stock material, the following process may be employed:

running-water is used for the immersion bath, in

The above and other objects andadvantages of the invention will be apparent from the following disclosure thereof, taken together with the annexed drawing which illustrates a certain form of embodiment thereof; which form is shown for the purpose of illustrating the invention, since the same has been found in practice to give satisfactory and reliable results.

In the drawing: Fig. -1 is a view in elevation, partly in section,

illustrating a spiral spring made in accordance with the invention; and

Fig. 2 is a top plan: view thereof; and

Fig. 3 is a diagrammatic sectional view 0f extrusion dies for carrying out a mode of the invention..

Referring now more particularly to the drawing, there is disclosed a spring indicated generally by the numeral I0 comprising a plurality of spirals or helixes H and terminating in the end loops I2, at ;an angle with relation to the spirals According to this invention, the spiral spring may be fabricated from plastic composition or from suitable tubular or rod plastic stock, which may be of any suitable cross-sectlonal'shape or form. The material preferably employed is one having thermoplastic characteristics, such as, for

Where the spiral spring is made from rod 01' order to prevent the water in the bath from approaching room temperature. v

Then the plastic stock material is withdrawn from the cold bath and immersed into a hot bath, the temperature of which is preferably just below boiling, for several hours, preferably from about one to three hours. The cold water immersion treatment of the plastic material prepares the latter for the hot water immersion treatment thereof. This latter treatment makes the material sufliciently flexible to be wound around a mandrel. 'The plastic stock material is then withdrawn from the hot bath and immediately wound into a spiral shape or form upon a suitable mandrel, the inside diameter of the spiral being determined by the diameter of the mandrel and the tension of the spirally wound device being regulated by the size of this inside diameter and the proximity of the adjacent spiral turns or loops.

It has been found economical to prepare ,a

: condition. It is understood that any other suitable liquid may be substituted for water.

. An economical method of making a spiral spring would be by injection molding, where the male and female plates are provided with complementary grooves, which together form the cavity or matrix for producing a finished product, and then the plastic composition is injected into the rooves in a conventional manner. steps or operations are required other than separating the plates and withdrawing the finished No further in transfer die Scan with facility be guided by the spiral groove or cavity I6, bearing in mind that the plastic material is pushed or forced forwardly in the direction of arrow II by hydraulic presissure. It is preferable to preheat transfer After the rod material is extruded from die it assuming the shape or cavity i6, it is cut into desired lengths and then the turns or loops are pressed together, assuming the form of the spirals I or loops H of Fig. 2, this being easily-done since the spiral-shaped rod pieces are still in soft semi.- plastic pliable state; the end loops H are formed and the completed spring is then immersed in cold water, thereby causing the material to set and the loops or turns of the spring to be maintained in their relative positions. A spiral spring made according to the above described extr'u- V it comes out of the transfer die I5.

It is understood that a plurality of spiral plastic springs either or the same size or different sizes maybe simultaneously molded by providing the required number of cavities in the mold, as well known in the art.

From the foregoing it is evident that there has been'herein provided, a helical spring comprising a plurality of connected loops formed. of a continuous piece of plastic materiaLsaid loops being displaceable relative to each other when brought under tension.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. The method of forming a spiral spring having a plurality of turns from thermoplastic material which consists in extruding the material in a heated state through a die part having an opening of a size equal to the cross-section of the material when extruded, guiding the extruded material through a spirally-arranged cavity having a pitch betweenadiacent turns greater than that of the finished spring, cutting the spirally formed material into lengths each having a plurality of turns therein after the same leaves said cavity,

bringing the adjacent turns of the cut spirally.

formed material into closer proximity to provide a spiral spring having the desired final pitch, forming end loops in each oi said lengths, and placing the spirally formed material in a cool i medium. I

2. In a method of forming a spiral spring hav; ing 'a plurality of turns from thermoplastic materiai, steps in said method which comprise passing rod material while in a heated semi-plastic state through a spirally arranged cavity having a pitch between adjacent turns greater than that of the finished spring, cutting the spirally formed material into lengths each having a plurality of turns therein after'the same leaves said cavity, bringing the adjacent turns of the spirally formed material into closer proximity to provide a spiral sprin having the desired final pitch, forming and loops in each .of said lengths, and placing the spirally formed material in a cool environment.

3. In a method of forming a spiral spring having a plurality of turns from plastic material,

steps in said method which comprise passing rod material while in a semi-plastic state through a spirally arranged cavity having a pitch between adjacent turns greater than that of the finished spring, cutting the spirally formed material into lengths each having a plurality of turns therein after' the same leaves said cavity, bringing the adjacent turns of the cut spirally formed material into closer proximity to provide a spiral spring having the desired final pitch, and hardening said spring. I

4. In amethod of forming a spiral spring having a plurality of turns, from plastic material,

steps in said method which comprise passing rod material while in a semi-plastic state through a spirally arranged cavity having a pitch between adjacent turns greater than that of the finished spring, cutting the spirally formed material into lengths each having a plurality of turns therein after the same leaves said cavity, bringing the adjacent turns of the cut spirally formed material into closer proximity to provide a spiral spring 7 having the desired final pitch, forming end loops in each of said lengths, and hardening said spring.

'rnnonoaa MAN. 

